1. Field of the Invention
This invention relates broadly to inductors for printed circuit boards. More particularly, this invention relates to inductor elements etched onto printed circuit boards.
2. State of the Art
It is known to generate inductor elements on a printed circuit board (PCB) by etching a pattern in a conductive layer of the PCB. Referring to prior art FIGS. 1 through 3, a printed circuit board 10 is shown having a non-conductive structural layer 12 and a conductive layer 14, which is typically made of copper. The conductive layer 14 is etched to provide circuit connection patterns 16 which function as inductor elements 18, 20, as well as lead traces (not shown). One particular application for this approach is to create a series inductor for decoupling the power to integrated circuits. One advantage of these etched inductor elements is that there is substantially no cost associated with their production, except for the surface area of PCB used for the inductor elements. This is because the inductor elements are generated during the normal etching process of the PCB.
The design latitude for etched inductor elements, however, is quite limited in inductance range. Furthermore, there are substantial trade-offs between PCB surface area, inductance, self-resonant frequency, and high frequency loss. For example, large inductance values (above 100 nH) require substantial surface area (greater than 0.2 in.sup.2). Moreover, a separate resistor component 22 is often required to control damping in an etched inductor element 20.